Title : Mechanistic Action of Hydroxyxanthone on Alleviation of Inflammation in human Intestinal Epithelium
Specific derivatives of synthetic hydroxyxanthrones (HDXs) have been shown to strengthen tight junction barrier and prevent tumor necrosis factor-α (TNF-α)-induced barrier disruption of intestinal epithelia. HDXs have been demonstrated to up-regulate the barrier-builder claudin-4 under both normal condition and TNF-α stimulation; however, little has been known regarding their mechanisms of action. As NFκB signal pathway was mostly related to regulation of barrier function, we therefore explored the mechanistic action of HDXs on alleviation of TNF-α induced inflammation in human intestinal epithelium. Caco2 cells as cell models cultured for 7 days were treated with different types of HDXs i.e. 1-monoHDX, 1,3-diHDX, 1,3,6-triHDX or 1,3,6,8-tetraHDX (100 mM) for 24 hours prior to TNF-α (100 ng/ml) exposure for another 24 hours. At the end of treatment, the total proteins were collected and analyzed for signaling proteins by Western blot technique. Incubation of Caco2 cells with HDXs did not alter the expression ratio to b-actin of NFκB, iκB, pMLC or MLCK proteins. In contrast, TNF-α administration decreased iκB and increased MLCK without change in NFκB and pMLC. Preincubation with HDXs was found to only decrease TNF-α induced increase in MLCK while the decreased ikB induced by TNF-α was not affected by HDXs. Collectively, various types of HDXs have an ability to attenuate the barrier dysfunction-stimulated by TNF-α through an inhibition of MLCK protein expression. The signaling mechanism responsible for the suppressive effect of HDXs on the TNF-α activated MLCK appears not to involve NFκB-iκB pathway. These findings may support the potential role of HDXs in protecting intestinal epithelial barrier from inflammation.